JP6645725B2 - Mold steel and mold - Google Patents

Description

  The present invention relates to a mold steel and a mold excellent in both high-temperature strength and heat conduction performance.

Conventionally, injection molding dies such as resin and rubber, die casting dies, hot press dies (also called hot stamping and die quenching), etc., are generally made by melting steel to form an ingot and then forging or rolling to block. And flat bars are machined and machined to form a mold, which is then subjected to heat treatment such as quenching and tempering.
In these dies, cooling is generally performed by providing a cooling circuit inside and circulating cooling water therethrough.

In such a mold, increasing the cooling efficiency by the cooling water leads to shortening of the cycle time, that is, improvement of productivity by increasing the cycle of product manufacturing (molding).
A simple way to increase the cooling efficiency is to bring the cooling circuit closer to the mold surface (design surface) of the mold.
However, in such a case, the mold becomes smaller due to a shorter distance between the cooling circuit and the molding surface, and a larger thermal stress is generated. Cracks) are likely to occur, which causes the mold life to be shortened.
Therefore, even if the cooling circuit is brought closer to the molding surface, there is naturally a limit there.

  As another method, it is conceivable that the cooling circuit is formed in an intricately meandering shape inside and outside the mold and the cooling capacity is increased by the overall shape and layout of the cooling circuit. In the method of manufacturing by cutting, the cooling circuit cannot be technically realized to have such a complicated shape.

Under these circumstances, in recent years, a technique of forming a mold by a layered manufacturing method (three-dimensional layered manufacturing method) has attracted attention.
The additive manufacturing method is a processing method in which three-dimensional model data is materialized by attaching materials. In the additive manufacturing method, first, a shape represented by three-dimensional CAD data is converted into a plurality of surfaces orthogonal to a predetermined axis. Calculates the cross-sectional shape of a slice generated by slicing, slices are actually produced, stacked and laminated, and the shape expressed by a computer is materialized.

In the additive manufacturing method, there are a case where a powder is used as a material and a case where a plate is used.
In the method using powder, the powder is spread in layers (the thickness of one layer is, for example, several tens of μm), and a certain area is irradiated with heat energy, for example, a laser beam or an electron beam, so that the powder layer is melt-solidified or sintered. Then, the whole shape is formed by further stacking these.

On the other hand, in additive manufacturing using a plate as a material, individual parts (plates) generated by slicing three-dimensional shape data in CAD are actually manufactured by machining, etc., and the parts are stacked and diffusion bonded etc. Forms the entire three-dimensional shape.
For example, Patent Documents 1 and 2 disclose an example of manufacturing a mold by this kind of additive manufacturing method.

  Specifically, Patent Document 1 below discloses an invention relating to “metal powder for powder sintering and lamination, a method for producing a three-dimensionally shaped object using the same, and a three-dimensionally shaped object to be obtained”. Irradiating a light beam to the powder material of the mold metal component to sinter or melt-solidify the powder at a predetermined location to form a solidified layer, and further form a solidified layer on the solidified layer obtained by this; Is repeated to produce a three-dimensionally shaped object.

  Patent Literature 2 below discloses an invention relating to “a mold nest, a method of manufacturing a mold nest, and a resin molding mold”, in which a nest having a spiral cooling path therein is manufactured. On the basis of the slice data, grooves for forming cooling paths are formed in the plurality of metal plates, the grooved metal plates are laminated in a predetermined order, and diffusion-bonded, and the obtained metal block is formed. The point of shaping is disclosed.

  The above-mentioned additive manufacturing method is to form the entire shape by stacking the materials, and it is possible to easily process and form even a complicated cooling circuit winding endlessly vertically and horizontally which can not be achieved by cutting work, Even if the cooling circuit is not intentionally brought closer to the molding surface of the mold than necessary, the cooling efficiency can be more effectively improved than that of the mold produced by cutting by conventional machining.

Conventionally, maraging steel or precipitation hardening stainless steel is generally used as a mold requiring high-temperature strength.
For this reason, even in Patent Document 1 described above, powder of such maraging steel or precipitation hardening stainless steel is used as a mold material.
Although these maraging steels and precipitation hardening stainless steels have sufficient high-temperature strength as molds, they contain a large amount of elements such as Si, Cr, Ni, and Co, which are easily dissolved in the matrix, and There is a problem that conduction performance (thermal conductivity) is low.

In a mold made by additive manufacturing, the cooling circuit can be freely made into a complicated shape.Thus, even if the mold material is made of maraging steel or precipitation hardening stainless steel, it can be made by additive manufacturing. Although the cooling circuit can be made into a complicated shape, the cooling effect can be increased by the shape effect of the cooling circuit, but it is difficult to increase the cooling efficiency to a sufficient level due to the low thermal conductivity of the material itself. .
Also, naturally, when a mold is manufactured by a conventional general manufacturing method without depending on additive manufacturing, the efficiency of cooling (heat exchange) becomes further insufficient.

On the other hand, as steel having high heat conduction performance (high heat conductivity), there are carbon steel and steel for machine structural use. These steels have a low content of elements such as Si, Cr, Ni, and Co, which are easily dissolved in the matrix, and exhibit high thermal conductivity because they are low alloy steels.
However, these steels have a problem that their high-temperature strength is low and their life when formed into a mold is short.
That is, regardless of whether or not a mold is formed by the additive manufacturing method, a mold steel that can realize sufficient high-temperature strength and heat conduction performance when formed into a mold has been conventionally provided. Did not.

  As another prior art to the present invention, Patent Literature 3 listed below discloses an invention relating to “die steel excellent in thermal fatigue properties”, in which the addition amounts of alloying elements Si and Cr are suppressed low, It is also disclosed that the balance between other alloy components is increased to increase the thermal conductivity and increase the softening resistance.

  As still another prior art, Patent Literature 4 listed below discloses an invention relating to “steel for molds”, in which the amounts of Si, Mn, and Cr are appropriately balanced to reduce the thermal conductivity of steel. It is disclosed that not only a desired value is effectively secured but also the machinability and impact value are sufficiently secured.

  As still another prior art, Patent Literature 5 listed below discloses an invention relating to “a steel for molds excellent in spheroidizing annealing property and quenching property”. It is disclosed that both the required hardenability and spheroidizing annealing required for the large-sized mold described above are imparted.

However, although the components described in Patent Documents 3 to 5 partially overlap the components of the steel for molds of the present invention in the range of the chemical components defined in the claims, the claims of the present invention are given as examples. Nothing satisfies the term, which is substantially different from the present invention.
Further, those described in Patent Documents 3 to 5 are not intended for additive manufacturing, and there is no mention of that point.

International Publication WO2011 / 149101 JP 2010-194720 A Japanese Patent No. 4992344 JP 2011-94168 A JP 2008-121032 A

  In view of the above circumstances, the present invention provides a mold steel capable of realizing both high-temperature strength and heat conduction performance when manufacturing a mold by applying the additive manufacturing method, and further provides such an additive manufacturing method The present invention provides a mold steel and a mold capable of realizing high high-temperature strength and heat conduction performance even when a mold is manufactured by machining a material obtained by processing an ingot. It was made for the purpose.

Claim 1 relates to a mold steel, which is expressed by mass% of 0.25 <C <0.38, 0.01 <Si <0.30, 0.92 <Mn <1.80, 0.8 <Cr ≦ 1.98, 0.8 <Mo <1.4, 0.25 < V <0.58, the balance being Fe and inevitable impurities, the thermal conductivity at 25 ° C. evaluated by the laser flash method is 31 W / m / K or more, and a die-casting machine with a mold clamping force of 135 tons is used. It has a steel structure in which the depth of wear of the spool core is less than 0.2 mm when 10,000 shot casting is performed.

  According to a second aspect, in the first aspect, the composition further contains 0.1 <Al <1.2 by mass%.

  According to a third aspect of the present invention, in any one of the first and second aspects, at least one of 0.30 <Ni ≦ 3.5 and 0.30 <Cu ≦ 1.5 by mass% is further contained.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the composition further contains 0.0001 <B ≦ 0.0050 by mass%.

  Claim 5 relates to any one of claims 1 to 4, wherein 0.003 <S ≦ 0.250, 0.0005 <Ca ≦ 0.2000, 0.03 <Se ≦ 0.50, 0.005 <Te ≦ 0.100, 0.01 <Bi ≦ 0.50, It is characterized by further containing at least one of 0.03 <Pb ≦ 0.50.

  Claim 6 further includes at least one of 0.004 <Nb ≦ 0.100, 0.004 <Ta ≦ 0.100, 0.004 <Ti ≦ 0.100, 0.004 <Zr ≦ 0.100 by mass% in any one of claims 1 to 5. It is characterized by doing.

  A seventh aspect of the present invention is characterized in that, in any one of the first to sixth aspects, at least one of 0.10 <W ≦ 4.00 and 0.10 <Co ≦ 3.00 by mass% is further contained.

According to an eighth aspect of the present invention, in any one of the first to seventh aspects, the material is used as a material for forming a mold by a layered manufacturing method.

According to a ninth aspect, in the eighth aspect , the material is a powder or a plate.

A tenth aspect relates to a metal mold, which is manufactured by an additive manufacturing method using the material according to any one of the eighth and ninth aspects.

The steel for molds according to the present invention is characterized by low or no addition of elements such as Si, Cr, Ni and Co to high alloy steels such as conventional maraging steel and precipitation hardening stainless steel. While increasing the thermal conductivity by alloying, the content of elements such as Mn, Mo, V, etc. is increased in the steel for machine structural use to increase the high-temperature strength. It has both properties of strength and thermal conductivity.
In addition, it maintains that it is a low alloy steel with a small amount of alloying elements as a whole.

In the steel for molds of the present invention, the content of Cr and Mo, which are quenchability improving elements, is reduced by machining, assuming that the mold may be manufactured by an additive manufacturing method. In the case of mold production, the content is suppressed to a small extent compared to the appropriate content. The alloy steel of the mold according to the present invention is reduced accordingly.
For example, JIS SKD61 is 5Cr and 1.5Mo, and JIS SKD7 is 3Cr and 3Mo.
In contrast, the mold steel of the present invention has Cr ≦ 1.98 and Mo <1.4.
Further, the range of the amount of Si + Mn + Cr + Mo + V of the present invention is less than 6.2, which is about 3 to 4% lower than the amount of Si + Mn + Cr + Mo + V of JIS SKD61 and JIS SKD7.

In the additive manufacturing method, particularly the additive manufacturing method using powder, when heat energy is applied to a layer in which the powder is laid to solidify the powder, the powder is melt-solidified or sintered.
At that time, the powder is rapidly cooled from a high temperature state such as a molten state, and quenching is automatically performed. And the quenching is performed rapidly under a high cooling rate. That is, quenching is performed sequentially and simultaneously in the process of laminating and molding the powder.
Since quenching is performed at a high cooling rate as described above, quenching can be performed well during additive manufacturing, even if the content of the hardenability improving component as a steel component is kept low in advance.
Further, the mold steel of the present invention has a high thermal conductivity due to its low alloy.

Although the mold steel of the present invention can be suitably used as a material for additive manufacturing, the mold steel of the present invention can also be used to create a mold shape by cutting a lump of steel by machining. It can also be used in the case of performing a die production. At this time, heat treatment conditions such as quenching may be determined according to the contained elements.
The mold thus obtained has high-temperature strength and high heat conduction performance due to the characteristics of the composition of the steel.

Next, the reasons for limiting each chemical component in the present invention will be described below. In addition, the value of each chemical component is mass%.
1) <Chemical component of claim 1>
0.25 <C <0.38
By setting 0.25 <C, when the mold obtained by machining the material obtained by processing the ingot is heat-treated, the hardness 30 to 57 HRC required for the mold is obtained. In addition, 30 to 57 HRC can be obtained even in a mold as manufactured by additive manufacturing. Furthermore, even when the mold after the additive manufacturing is heat-treated, 30 to 57 HRC can be obtained. In any of the molds manufactured by any of the manufacturing methods, the hardness is insufficient when C ≦ 0.25. On the other hand, when 0.38 ≦ C, the thermal conductivity decreases.

0.01 <Si <0.30
When Si ≦ 0.01, the machinability deteriorates significantly. On the other hand, when 0.30 ≦ Si, the thermal conductivity significantly decreases.

0.92 <Mn <1.80
When Mn ≦ 0.92, the hardenability when quenching a mold manufactured by machining with respect to a material obtained by processing an ingot or when quenching a mold manufactured by additive manufacturing is insufficient. On the other hand, when 1.80 ≦ Mn, the thermal conductivity decreases. When 1.80 ≦ Mn, tempering embrittlement occurs when P is high. A more preferred range is 0.92 <Mn <1.50.

0.8 <Cr ≤1.98
When Cr ≦ 0.8, the weather resistance is insufficient. When Cr ≦ 0.8, the ductility at 200 to 350 ° C. is reduced due to blue embrittlement. Furthermore, when Cr ≤ 0.8, the hardenability is insufficient when quenching a mold manufactured by machining to the material obtained by processing the ingot or when quenching a mold manufactured by additive manufacturing. I do. On the other hand , excessive addition lowers the thermal conductivity, so the upper limit of Cr is set to 1.98.

0.8 <Mo <1.4
At Mo ≤ 0.8, the mold produced by machining the ingot was quenched and tempered, or the mold produced by additive manufacturing was tempered (with or without quenching). ), It is difficult to secure hardness by secondary curing, and the high-temperature strength becomes insufficient. On the other hand, when 1.4 ≦ Mo, the decrease in fracture toughness value is large.

0.25 <V <0.58
In the case of V ≦ 0.25, coarsening of austenite crystal grains when quenching a mold manufactured by machining to a material obtained by processing an ingot or when quenching a mold manufactured by additive manufacturing Is a problem. In addition, when V ≦ 0.25, a mold obtained by machining a material obtained by processing an ingot was quenched and tempered, or a mold manufactured by additive manufacturing was tempered (there was quenching). ), It is difficult to secure the hardness by the secondary curing, and the high temperature strength becomes insufficient. On the other hand, when 0.58 ≦ V, the above effect tends to be saturated and the cost is increased.
Also, when 0.58 ≦ V, when mold material is manufactured by a normal manufacturing method (melting → refining → casting → hot working), a large amount of coarse VC crystallizes in an ingot at the time of solidification of casting. Is more likely to be the starting point of mold destruction.

In the steel of the present invention, the following components can be usually contained as inevitable impurities in the following amounts.
N ≦ 0.05
P ≦ 0.05
S ≦ 0.003
Cu ≦ 0.30
Ni ≦ 0.30
Al ≦ 0.10
W ≦ 0.10
O ≦ 0.01
Co ≦ 0.10
Nb ≦ 0.004
Ta ≦ 0.004
Ti ≦ 0.004
Zr ≦ 0.004
B ≦ 0.0001
Ca ≦ 0.0005
Se ≦ 0.03
Te ≦ 0.005
Bi ≦ 0.01
Pb ≦ 0.03
Mg ≦ 0.02

2) <Chemical component of claim 2>
The steel of the present invention may undergo quenching after additive manufacturing. To suppress coarsening of austenite grains during quenching
0.1 <Al <1.2
Can be contained.
Al combines with N to form AlN, and has an effect of suppressing the movement of austenite crystal grain boundaries (that is, grain growth).
In addition, since Al forms nitrides in steel and contributes to precipitation strengthening, it also has an effect of increasing the surface hardness of the nitrided steel material. It is effective to use a steel material containing Al for a mold (including parts constituting a part of the mold) which is subjected to nitriding treatment for higher wear resistance.

3) <Chemical component of claim 3>
In recent years, the size of a mold tends to increase due to enlargement and integration of mold parts. Large molds are difficult to cool. For this reason, when quenching a large mold of a steel material having low quenchability, ferrite, pearlite, and coarse bainite precipitate during quenching, and various characteristics deteriorate. Such concerns may be dealt with by increasing the hardenability by selectively adding Cu-Ni. In particular,
0.30 <Ni ≦ 3.5
0.30 <Cu ≦ 1.5
May be contained.
Ni also has an effect of bonding with Al to precipitate an intermetallic compound and increase hardness. Cu also has the effect of increasing hardness by aging precipitation. The preferred range is
0.50 ≦ Ni ≦ 3.0
0.50 ≦ Cu ≦ 1.2
It is. When any of the elements exceeds a predetermined amount, segregation becomes remarkable, resulting in a decrease in mirror polishing property.

4) <Chemical component of claim 4>
As a measure for improving the hardenability, the addition of B is also effective. Specifically, if necessary
0.0001 <B ≦ 0.0050
Is contained.
Since B has no effect of improving hardenability when BN is formed, B alone needs to be present in steel. Specifically, it is only necessary to form a nitride with an element having a higher affinity for N than B and not to combine B and N. Examples of such elements include Nb, Ta, Ti, Zr, and the like. Although these elements have the effect of fixing N even if they are present at the impurity level, depending on the amount of N, it may be preferable to add them within the range of claim 6 described later.

5) <Chemical component of claim 5>
Since the steel of the present invention has a small amount of Si, the machinability is slightly poor. As a measure for improving workability, the following S, Ca, Se, Te, Bi, and Pb may be selectively added. In particular,
0.003 <S ≦ 0.250
0.0005 <Ca ≦ 0.2000
0.03 <Se ≦ 0.50
0.005 <Te ≦ 0.100
0.01 <Bi ≦ 0.30
0.03 <Pb ≦ 0.50
May be contained.
If any of the elements exceeds a predetermined amount, it leads to saturation of machinability, deterioration of hot workability, impact value and mirror polishing property.

6) <Chemical component of claim 6>
If the quenching heating temperature is increased or the quenching heating time is prolonged due to unexpected equipment trouble or the like, deterioration of various characteristics due to coarsening of crystal grains is concerned. In preparation for such a case, Nb, Ta, Ti, and Zr are selectively added, and coarsening of austenite crystal grains can be suppressed by fine precipitates formed by these elements. In particular,
0.004 <Nb ≦ 0.100
0.004 <Ta ≦ 0.100
0.004 <Ti ≦ 0.100
0.004 <Zr ≦ 0.100
May be contained.
When any of the elements exceeds a predetermined amount, carbides, nitrides, and oxides are excessively generated, and the impact value and the mirror polishing property are reduced.

7) <Chemical component of claim 7>
An increase in C is effective for increasing the strength. However, an excessive increase in C causes deterioration of characteristics (impact value and mechanical fatigue characteristics) due to an increase in carbide. In order to increase the strength without causing such a problem, W or Co may be selectively added.
W increases the strength by fine precipitation of carbides. Co increases the strength by solid solution in the base material, and also contributes to precipitation hardening through change in carbide morphology. In particular,
0.10 <W ≦ 4.00
0.10 <Co ≦ 3.00
May be contained.
When any of the elements exceeds a predetermined amount, the characteristics are saturated and the cost is significantly increased. The preferred range is
0.30 ≦ W ≦ 3.00
0.30 ≦ Co ≦ 2.00
It is.

  According to the present invention, it is possible to provide a mold steel and a mold capable of realizing both high-temperature strength and thermal conductivity.

It is sectional drawing of the die-casting die which has a spool core of one Embodiment of this invention. It is a figure showing a worn state of a spool core.

Next, examples of the present invention will be described in detail below.
Powders of 17 types of steel having the chemical compositions shown in Table 1 were produced by a gas atomization method, and a three-dimensional additive manufacturing method using a laser irradiation was performed using the powders to form a partial mold that was part of a die casting mold 10 shown in FIG. Was manufactured. The spool core 12 has a cooling circuit 14 formed therein. Here, the cooling circuit 14 has a spiral three-dimensionally complicated shape.

In Table 1, Comparative Example 1 is hot die steel SKD61, Comparative Example 2 is 18Ni maraging steel, Comparative Example 3 is martensitic stainless steel SUS420J2, and Comparative Example 4 is mechanical structure steel SCM435.
In addition, although each of the invention examples in Table 1 may contain an unavoidable amount of impurity components, they are not described in the table.

In FIG. 1, a die casting mold 10 has a fixed mold 16 and a movable mold 18. A cavity 20 as a molding space for the product and a runner 22 are provided between them, and they are connected by a narrow gate 24.
The spool core 12 is arranged at a position sandwiching a cylindrical biscuit portion 28 which is a final solidification position of a casting together with the plunger 26. The runner 22 extends from the biscuit portion 28.
A groove is formed in the spool core 12, and a part of the runner 22 is formed in the groove.

  The mold obtained in the above procedure was heated (tempered or aged) to a temperature in the range of 350 to 650 ° C. and tempered to 43 HRC. Then, it was finished to the final mold shape by machining. The die is a spool core 12 of a 135-ton die casting machine. The position of the spool core 12 in the mold structure is shown in FIG. Here, FIG. 1 is a cross-sectional view of a die-casting mold structure viewed from the side.

The cycle of die casting is a cycle of mold clamping → injection → die timer → mold opening → product removal → air blow → release agent spray → air blow (Fig. 1 shows the process of the die timer).
First, the movable mold 18 comes into contact with the fixed mold 16 to be in a mold clamped state. At this time, a cavity 20 is formed as a product molding space. In this state, a molten metal of an aluminum alloy (hereinafter, referred to as an aluminum alloy) is poured into the sleeve 30 with a ladle, and the molten metal is injected by the plunger 26 moving at a high speed.
The injected molten metal moves through the runner 22 and flows into the cavity 20 from the gate 24 in a liquid, granular, or mist state. It is easy to understand if you imagine a water gun or spray. Eventually, the cavity 20 is filled with the molten metal. Then, pressure is applied to the molten metal that fills the cavity 20 to wait until it is solidified.

  This is a process called a di-timer, and FIG. 1 shows this state. When the molten metal is solidified into a product, the movable mold 18 is moved to open the mold. The product is removed using an extrusion pin or manipulator. The mold that has been in contact with the high-temperature aluminum alloy has a high temperature, and is cooled by air blowing and spraying a release agent. This is one cycle of die casting.

  In the above process, shortening of the die timer (the process of solidifying the molten metal in the mold) was studied. If the cooling capacity of the spool core 12 is high, the die timer can be shortened because the biscuit portion 28 solidifies quickly, and therefore the overall cycle time can be shortened. Reducing the cycle time is very preferable from the viewpoint of improving productivity.

For the test, a die casting machine with a mold clamping force of 135 tons was used. From the state where the die timer was sufficiently long (the state where the biscuit part 28 was completely solidified), the die timer was shortened by one second, and the biscuit part 28 was opened when the mold was opened. It was judged as pass if solidified and failed if not. Then, the shortest die timer that passed was evaluated.
The shape of the biscuit portion 28 is φ50 × 40 mm, and the distance between the water cooling hole 14 of the spool core 12 and the surface is 15 mm. The melt is ADC12 at 730 ° C. and the weight of the casting is 660 g. Further, it was also evaluated whether or not remarkable wear was observed on the spool core 12 after the 10,000 shot casting. If the high-temperature strength is insufficient, wear due to the flow of the molten metal becomes remarkable, and the life of the mold cannot be ensured.

Table 2 shows the test results. The goal is that there is no wear with a depth of 0.2 mm or more after 10,000 shots for the die timer and 10 [seconds] or less.
The die timers of Comparative Examples 1 to 3 are as long as 12 to 14 seconds. This is because the heat conductivity is as low as 23 [W / m / K] or less, and heat exchange is difficult to be performed.

On the other hand, there was no remarkable wear on the spool core 12 after the 10,000 shot casting. This is because they have sufficient high-temperature strength.
In the case of Comparative Example 4 in which the thermal conductivity was as high as 38 [W / m / K], the die timer was as short as 8 [seconds], which is a favorable result. It was observed that it was difficult to secure the mold life. This is shown in FIG. In the groove M that forms a part of the runner 22, near the corner k where the direction of the flow of the molten metal changes abruptly, dripping skin is observed due to wear.

  The thirteen examples of the invention have very short die timers of 9 [seconds] or less. This is because the heat conductivity is as high as 31 [W / m / K] or more, and heat exchange is easily performed. In addition, since the spool core 12 had sufficient high-temperature strength, there was no significant wear on the spool core 12 after 10,000 shot casting. There were no cracks from the water cooling holes in both the comparative example and the invention example.

  Next, it was verified whether the die timer could be reduced by half even in Comparative Examples 1 to 3. Specifically, in order to promote heat exchange, a spool core 12 in which the distance between the water cooling hole 14 and the surface was reduced to 7.5 mm was produced, and a test was performed under the same conditions as the test in Table 2. The results are shown in Table 3. The die timer was shortened to the same level as the invention example in Table 2. The mold structure in which the water cooling holes 14 are brought close to the surface is extremely effective for shortening the die timer.

  On the other hand, cracks from the water cooling holes 14 penetrated the surface before the 10,000 shot casting was completed, and the life was extended. This is because the thermal stress increased in addition to the shortening of the crack penetration distance. Even if the die timer is shortened, it is difficult to improve the productivity of die casting (since it takes a long time to change the mold). Although 10,000 shots were not achieved, the wear was not remarkable as in the case of the test in Table 2.

  As can be seen from the above, in the invention example, the die timer can be shortened while preventing the abrasion and the water-cooling hole cracking and ensuring the mold life. In the comparative example, if the die life is ensured, the die timer becomes longer, and if the die timer is shortened, the die life cannot be ensured. The reason why the invention example can achieve both the securing of the mold life and the shortening of the die timer is that both the high-temperature strength and the thermal conductivity are high.

The embodiment of the present invention has been described above in detail, but this is merely an example.
The steel of the present invention, which has both high thermal conductivity and high-temperature strength, is suitable not only for a die-casting die but also for a resin injection-molding die. It also exhibits high performance as a mold for hot pressing (also called hot stamping or die quench) of steel sheets. At this time, even if the steel of the present invention is applied to mold manufacturing by ordinary machining and heat treatment instead of additive manufacturing, the mold life is ensured and cycle is improved compared to the conventional steel mold of the same shape made by the same manufacturing method. It is effective for shortening.
Further, it is also effective to combine the metal mold of the present invention with surface modification (shot blast, sand blast, nitriding, PVD, CVD, plating, etc.).
Further, the steel of the present invention can be used as a welding material in a state of a rod or a wire. Specifically, using the welding material for mold steel according to the present invention, a mold manufactured by additive manufacturing, or a mold manufactured by machining a material obtained by processing an ingot by machining. Alternatively, welding repair can be performed. In this case, the chemical composition of the mold to be repaired may be different from the range of the steel of the present invention, or may be within the range of the steel of the present invention. In any case, the part repaired by the welding material of the steel of the present invention has high high-temperature strength and high thermal conductivity exhibited by the components of the steel of the present invention.
In addition, the present invention can be implemented in a form in which various changes are made without departing from the spirit thereof.

10 Die casting mold 12 Spool core 14 Cooling circuit

Claims (10)

By mass%
0.25 <C <0.38
0.01 <Si <0.30
0.92 <Mn <1.80
0.8 <Cr ≦ 1.98
0.8 <Mo <1.4
0.25 <V <0.58
The balance has the composition of Fe and unavoidable impurities,
When the thermal conductivity at 25 ° C. evaluated by a laser flash method is 31 W / m / K or more, and a 10,000-shot casting is performed using a die-casting machine having a mold clamping force of 135 tons, the depth of wear of the spool core is reduced. Having a steel structure of less than 0.2 mm. By mass%
0.1 <Al <1.2
The steel for molds according to claim 1, further comprising: By mass%
0.30 <Ni ≦ 3.5
0.30 <Cu ≦ 1.5
The mold steel according to claim 1, further comprising at least one of the following. By mass%
0.0001 <B ≦ 0.0050
The mold steel according to any one of claims 1 to 3, further comprising: By mass%
0.003 <S ≦ 0.250
0.0005 <Ca ≦ 0.2000
0.03 <Se ≦ 0.50
0.005 <Te ≦ 0.100
0.01 <Bi ≦ 0.50
0.03 <Pb ≦ 0.50
The mold steel according to any one of claims 1 to 4, further comprising at least one of the following. By mass%
0.004 <Nb ≦ 0.100
0.004 <Ta ≦ 0.100
0.004 <Ti ≦ 0.100
0.004 <Zr ≦ 0.100
The mold steel according to any one of claims 1 to 5, further comprising at least one of the following. By mass%
0.10 <W ≦ 4.00
0.10 <Co ≦ 3.00
The mold steel according to any one of claims 1 to 6, further comprising at least one of the following.   The mold steel according to any one of claims 1 to 7, which is used as a material for forming a mold by an additive manufacturing method.   The mold steel according to claim 8, wherein the material is a powder or a plate.   A mold manufactured by the additive manufacturing method using the material according to claim 8.